Electrofusion has developed into an extremely efficient method for the fusion of mammalian cells, mainly because of its mild conditions, which result in a high number of viable fusion products [see e.g. White, K. L. 1995, Electrofusion of mammalian cells, Methods in Molecular Biology, 48, 283-293]. The application of an electrical field over phospholipid bilayer membranes induces pore formation when the applied potential reaches or exceeds the membrane breakdown potential. Consequently, electro-permeabilization techniques has been used in a wide variety of biological experiments, like electrofusion for the creation of hybridomas and new cell lines [see e.g. Zimmermann, U., et al., 1985, Electrofusion: a novel hybridization technique, Adv. Biotechnol. Proc. 4, 79-150; Neil, G. A. et al., 1993. Electrofusion, Methods in Enzymology, 220, 174-196; Glassy, M. 1988, Product review: Creating hybridomas by electrofusion, Nature, 333, 579-580], in vitro fertilization [see e.g. Ogura, A. et al., 1995, Spermatids as male gametes. Reprod. Fertil. Dev., 7, 155-159], cloning experiments [see e.g. Van Stekelenburg-Hamers, A. E. P., et al., 1993, Nuclear transfer and electrofusion in bovine in vitro-matured/in vitro-fertilized embryos: effect of media and electrical fusion parameters, Mol. Reprod. Dev., 36, 307-312], electroporation of cells for introduction of cell-impermeant solutes [see e.g. Electroporation: a general phenomenon for manipulating cells and tissues, J. Cell. Biochem., 51: 426-435; Li, H., et al., 1997, Transfection of rat brain cells by electroporation, J. Neurosci. Methods, 75, 29-32; Lundqvist, J. A., et al., 1998, Altering the biochemical state of individual cultured cells and organelles with ultramicroelectrodes, Proc. Natl. Acad. Sci. USA, 95, 10356-10360], and electro-insertion for the addition of membrane-associated macromolecules, including proteins [see e.g. Mouneimne, Y., et al., 1989, Electro-insertion of xeno-glycophorin into the red blood cell membrane, Biochem. Biophys. Res. Com. 159, 34-40]. Applications of in vivo electrofusion include the incorporation of gonococcal attachment receptors from human HL60 cells to rabbit corneal epithelial tissue as a viable model of human-specific pathogens [see e.g. Heller, R., et al., 1990, Transfer of human membrane surface components by incorporating human cells into intact animal tissue by cell-tissue electrofusion in vivo, Biochim. Biophys. Acta, 1024, 185-188].
Electric-field-induced fusion is widely employed in biomedical research for a population of cells in suspension. Cells are first brought into contact by dielectrophoresis through the application of a low-amplitude, high-frequency AC field and subsequently a fraction of the cells are fused by a strong and short DC pulse. Bulk electrofusion of large quantities of cells is useful for creating and selecting new cell lines, but cannot be applied to fuse single cells with high precision. This leads to unwanted fusion between cells from the same cell-line, as well as the wanted fusion between cells from different cell lines. Furthermore, bulk electrofusions do not allow the control over the number of cells that are to be fused together, which leads to unfavorable ratios of dinuclear-to-multinuclear fusion products.